The present invention relates to a tire having a rubber tread of a lug and groove configuration and which may be of a co-extruded cap/base construction; wherein at least a part of the visible portion of the tread is exclusive of carbon black and thereby of a color other than black. Such non-black colored rubber includes the outer surface of at least one of said tread lugs intended to be ground-contacting. In one aspect of the invention, said non-black colored rubber composition contains
(A) a precipitated silica reinforcement which has been pre-treated with a hydrophobation agent and optionally also pre-treated with a coupling agent or
(B) a precipitated silica which has been pre-treated with a hydrophobating agent and a coupling agent which does not from an alcohol byproduct upon reacting with hydroxyl groups (e.g. silanol groups) contained on the surface of said precipitated silica. In another aspect of the invention, said non-black colored rubber composition is comprised of at least one diene based elastomer and a brominated poly(isobutylene-co-para-methylstyrene) where a coupling agent for said silica is an organo phosphite.
Tires are typically provided with its various components as various rubber compositions which contain carbon black reinforcement and which are therefore black in color.
Most tires have a tread of a lug and groove configuration, of which many tires are of a cap/base construction of for which the rubber tread cap contains the lug and groove configuration wherein the outer surfaces of the lugs are designed to be ground-contacting and for which the rubber tread base underlies the tread cap. Such cap/base tire construction and such tread lug and groove configuration are well known to those having skill in such art.
However, it remains desirable for some purposes to provide a tire with a tread of which at least a portion is of a non-black color so that the resulting tread is of a non-black color of a multiplicity of colors.
For purposes of this invention, it is intended to provide a black colored tread of lug and groove configuration which is further configured with at least a portion of the visible surface of said tread is of a non-black color, preferably a color which contrasts with black. Thus the visible portion of the tire tread is of at least two different visible colors which may be black and at least one additional color.
It is appreciated that it is also desired to provide a tire with a tread with appropriate wear and traction characteristics and it is often difficult to provide a tire tread with segments of differing rubber compositions, as would be utilized in a case of a tire tread with road-contacting segments of contrasting colors, which have the same or very similar wear and traction. For example, see PTC patent application WO 99/01299.
Also, historically, a typical example of a component of a tire having a color which contrasts with the conventional black color of the tire is a tire sidewall in which a portion of the rubber is white in color resulting from a blend of rubber and titanium dioxide pigment in the absence of, or exclusive of, particulate carbon black reinforcement. Indeed, tires with white colored portions of their sidewalls are well known.
However, for tire treads, it is also appreciated that coloring pigments such as titanium dioxide, by itself, does not provide significant rubber reinforcement equivalent to rubber reinforcing carbon black. Therefore, such white colored tire components are conventionally limited to rubber compositions which do not need such a high degree of reinforcement such as for example, outer, visible, portions of tire sidewalls.
It is also appreciated that many non-black colored rubber composition for tire components, particularly white sidewall components have a tendency to discolor as a result of various discoloring chemicals which may be contained in various rubber compositions which are adjacent to the colored rubber composition. Accordingly, it is a common practice to use substitute non-discoloring chemicals for discoloring chemicals in such adjacent rubber compositions such as for example, non-discoloring antidegradants and non-discoloring rubber processing oils. Such practice is well known in the tire white sidewall art.
In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d if used herein, may be used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d, if used herein, are used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably unless otherwise indicate. The terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d may be used interchangeably unless otherwise indicated.
In accordance with this invention, a tire having a tread comprised of at least one non-black colored, exclusive of carbon black, rubber composition, wherein said tread is of a co-extruded cap/base construction; wherein said tread cap is configured with lugs and grooves; wherein said tread cap is comprised of said non-black colored rubber composition comprised of, based upon parts by weight per 100 parts by weight elastomer(s), (phr):
(A) 100 phr of elastomer comprised of
(1) about 5 to about 80, alternately about 10 to about 50, phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or iodine, preferably bromine,
(2) about 20 to about 95, alternately about 50 to about 90, phr of at least one diene-based elastomer and
(B) about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of synthetic amorphous silica aggregates, wherein said silica aggregates contain hydroxyl groups (e.g. silanol groups) on their surface; and
(C) about 0.5 to about 25, preferably about 1 to about 15, phr of at least one organo phosphite selected from monophosphites selected from formula (I) and diphosphites selected from formula (II) and diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite, preferably monophosphites of formula (I): xe2x80x83((OR4)2xe2x80x94Pxe2x80x94Oxe2x80x94R5)2xe2x80x94R6xe2x80x83xe2x80x83(II)
wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals; wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, wherein R5 is a phenyl radical; and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms;
wherein said organo phosphite is preferably the organo phosphite of formula (I)
wherein said organo phosphite is provided by one or more of the following:
(a) by mixing said organo phosphite with said elastomer(s) and said synthetic silica in an internal rubber mixer,
(b) by pre-reacting said halogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
(c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphite/silica composite thereof,
(d) mixing said organo phosphite with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, according to any of said steps (a), (b) or (c), wherein said synthetic silica includes pre-hydrophobated silica aggregates which have been pre-hydrophobated prior to mixing with said elastomers with an alkylsilane of formula (III),
(e) mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (III) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
(f) by pre-reacting said organo phosphite and said alkylsilane of Formula (III), and optionally an organomercaptosilane of the general formula (IV), with
(i) said aggregates of synthetic precipitated silica or
(ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof,
wherein said alkylsilane of the general Formula (III) is represented by
xe2x80x83Xnxe2x80x94Sixe2x80x94R4xe2x88x92nxe2x80x83xe2x80x83(III)
wherein R is an alkyl radical having from one to 18 carbon atoms, n is a value of from 1 to 3 and X is a radical selected from chlorine or bromine or alkoxy radical as (OR1)xe2x80x94, wherein R1 is an alkyl radical selected from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (IV):
(X)n(R2O)3xe2x88x92nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(IV)
wherein X is a radical selected from chlorine, bromine, and alkyl radicals having from one to 16 carbon atoms; wherein R2 is an alkyl radical having from one to 16 carbon atoms and R3 is an alkylene radical having from one to 16 carbon atoms; and n is a value from zero to 3.
In further accordance with this invention, said tire tread cap is composed of from three to five co-extruded transverse sections, each section positioned circumferentially around the tire and extending from one peripheral edge of the tread to the other, namely, two, spaced apart outboard tire tread cap sections each section including about 10 to about 40 percent of the tire tread cap and from one to three, preferably one, tire tread cap sections positioned in the central portion of the tire tread cap and between said outboard tire tread cap sections; where at least one of said central tire tread cap sections is of a non black-colored, exclusive of carbon black, rubber composition and said two outboard tire tread rubber compositions are of said black colored, carbon black-containing, rubber composition.
In the practice of this invention, said rubber composition may also contain an additional coupling agent as, for example, an alkoxysilyl polysulfide such as for example, a bis(3-trialkoxysilylalkyl) polysulfide wherein alkyl radicals for said alkoxy groups are selected from one or more of methyl and ethyl radicals, preferably an ethyl radical and the alkyl radical for said silylalkyl component is selected from butyl, propyl and amyl radicals, preferably a propyl radical and wherein said polysulfide component contains from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Representative of such other coupling agents are, for example, bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Such additional coupling agent may, for example, be added directly to the elastomer mixture or may be added as a composite of precipitated silica and such coupling agent formed by treating a precipitated silica therewith or by treating a colloidal silica therewith and precipitating the resulting composite.
In further accordance with this invention, said tire is provided wherein at least one component thereof is in contact with said non-black colored sidewall and/or non-black colored groove is of a black colored rubber comprised of said non-black colored rubber composition, wherein, however, said particulate reinforcing filler is comprised of about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of about 25 to about 100, optionally about 35 to about 90, phr of particulate reinforcing filler comprised of
(A) from zero to about 100, alternately about 10 to about 85, phr of synthetic amorphous silica aggregates and, correspondingly,
(B) from zero to about 75, alternately about 10 to about 60 phr of at least one of carbon black and silica treated carbon black having domains of silica on its surface.
wherein said silica aggregates contain hydroxyl groups (e.g. silanol groups) on their surface.
A significant aspect of this invention is the use of a reaction product of said organo phosphite and a said halogenated (preferably brominated) copolymer of isobutylene and p-methyl styrene in order to improve the polymer (e.g. elastomer) to filler interaction (via reaction of the organo phosphite with the halogen of the halogenated copolymer of isobutylene and p-methyl styrene) to thereby enhance resulting rubber composition properties leading to enhanced tire component (e.g. tire tread) properties including aged performance such as, for example durability and/or stability properties.
Representative examples of organo phosphites understood to be commercially available are, for example for example, triisodecyl phosphite, trilauryl phosphite, tris(tridecyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, triphenyl phosphite, triisononylphenyl phosphite, trimethyl phosphite, triethyl phosphite, tris (2-chloroethyl) phosphite, triisopropyl phosphite, tributyl phosphite, triisooctyl phosphite and tris (2-ethylhexyl) phosphite, as well as tris (2,4-dit-butylphenyl) phosphite, and bis 2,4,6,tri-t-butylphenyl 2-butyl-2-ethyl-1,3-propanediol phosphite; and diphosphites as, for example, distearyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6,di,t-butyl4-methylphenyl pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol diphosphite and mixtures thereof.
In practice, the synthetic amorphous silica may be selected from aggregates of precipitated silica, which is intended to include precipitated aluminosilicates as a co-precipitated silica and aluminum, and from fumed (pyrogenically formed) silica.
Such precipitated silica is, in general, well known to those having skill in such art. For example, such precipitated silica may be precipitated by controlled addition of an acid such as, for example, hydrochloric acid or sulfuric acid, to a basic solution (e.g. sodium hydroxide) of a silicate, for example, sodium silicate, usually in the presence of an electrolyte, for example, sodium sulfate. Primary, colloidal silica particles typically form during such process which quickly coalesce to form aggregates of such primary particles and which are then recovered as precipitates by filtering, washing the resulting filter cake with water or an aqueous solution, and drying the recovered precipitated silica. Such method of preparing precipitated silica, and variations thereof, are well known to those having skill in such art.
The silica treated carbon black relates to carbon black which contains domains of exposed silica on the surface of the carbon black. Such carbon black may be prepared, for example, by reaction of an alkyl silane (e.g. an alkoxy silane) with carbon black or by co-fuming carbon black and silica at an elevated temperature. For example, see U.S. Pat. Nos. 5,679,728 and 6,028,137.
It is preferred that an in situ reaction of said organo phosphite and silica, optionally including the alkylsilane of formula (III), within the elastomer host may be accomplished without an evolution of an alcohol as compared to using the aforesaid alkoxysilyl polysulfide coupling agent by the inherent chemistry of the organo phosphite material and hydroxyl groups contained on the surface of said silica material in which water evolved instead of an alcohol as a byproduct of the reaction.
In the further practice of the invention, the aforesaid in situ reaction of said organo phosphite silica material within the elastomer host via said internal rubber mixing process is accomplished wherein said silica material is a precipitated silica and/or silica-containing carbon black which is hydrophobated prior to its addition to the elastomer (pre-hydrophobated). Such in situ reaction is considered herein to be important as to both the process of mixing and reacting of the organo phosphite and pre-hydrophobated silica material as to a resulting product thereof. In particular, is it considered herein that pre-hydrophobation of the silica material, particularly with an alkyl silane of the general formula (III) enables a more efficient mixing, or processing, of it within the elastomer host in that such pre-hydrophobation of the silica material
(A) renders it more compatible with the diene-based elastomer and
(B) substantially reduces a tendency for a precipitated silica to agglomerate with itself within the elastomer host.
In the practice of this invention, said pre-hydrophobated precipitated silica aggregates may be pre-hydrophobated, for example, by treating silica in an aqueous colloidal form thereof with said alkylsilane of Formula (III).
The hydrophobated precipitated silica aggregates might be recovered, for example, from said treated colloidal silica, for example as a treated silica hydrosol, with the aid of acid addition to the treated colloidal silica (for example, sulfuric acid or hydrochloric acid) followed by water washing and drying the recovered hydrophobated silica as a hydrophobated silica gel or as a hydrophobated precipitated silica. While this invention is not intended to be directed to a specific preparation technique (preparation of silica hydrosols, recovery of silica gels and precipitated silicas, etc.) of the pre-hydrophobated precipitated silica itself, for education purposes in this regard, reference might be made to U.S. Pat. Nos. 5,094,829 as well as 5,708,069, 5,789,514 and 5,750,610 for a more detailed discussion.
Representative alkylsilanes of Formula (III) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.
Representative organomercaptosilanes of formula (IV) are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
In practice, various diene-based elastomers may be used such as, for example, homopolymers and copolymers of monomers selected from isoprene and 1,3-butadiene and copolymers of at least one diene selected from isoprene and 1,3-butadiene and a vinyl aromatic compound selected from styrene and alphamethyl styrene, preferably styrene.
Representative of such conjugated diene-based elastomers are, for example, cis 1,4-polyisoprene (natural and synthetic), cis 1,4-polybutadiene, styrene/butadiene copolymers (aqueous emulsion polymerization prepared and organic solvent solution polymerization prepared), medium vinyl polybutadiene having a vinyl 1,2-content in a range of about 15 to about 90 percent, isoprene/butadiene copolymers, styrene/isoprene/butadiene terpolymers. Tin coupled elastomers may also be used, such as, for example, tin coupled organic solution polymerization prepared styrene/butadiene co-polymers, isoprene/butadiene copolymers, styrene/isoprene copolymers, polybutadiene and styrene/isoprene/butadiene terpolymers.
The brominated poly(isobutylene-co-para-methylstyrene) polymer may be obtained, for example, as Exxpro 3745, a trademark of the ExxonMobil Chemical Company.
While commonly employed synthetic amorphous silica, or siliceous pigments, used in rubber compounding applications can be used as the silica in this invention, including precipitated siliceous pigments and fumed (pyrogenic) silica, as earlier presented herein said silica is preferably in a form of aggregates of a synthetic, amorphous precipitated silica.
The precipitated silica aggregates preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate and may include co-precipitated silica and a minor amount of aluminum.
Such silicas might usually be characterized, for example, by having a BET surface area, as measured using nitrogen gas, preferably in the range of about 40 to about 600, and more usually in a range of about 50 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).
The silica may also be typically characterized by having a dibutylphthalate (DBP) absorption value in a range of about 50 to about 400 cm3/100 g, and more usually about 100 to about 300 cm3/100 g.
Various commercially available precipitated silicas may be considered for use in this invention such as, only for example herein, and without limitation, silicas from PPG Industries under the Hi-Sil trademark with designations Hi-Sil 210, Hi-Sil 243, etc; silicas from Rhodia as, for example, Zeosil 1165MP and Zeosil 165GR, silicas from J. M. Huber Corporation as, for example, Zeopol 8745 and Zeopol 8715, silicas from Degussa AG with, for example, designations VN2 and VN3, as well as other grades of silica, particularly precipitated silicas, which can be used for elastomer reinforcement.
In practice, a purpose of a coupling agent is to aid in enabling said amorphous silica to reinforce the rubber composition, although in a case where said pre-hydrophobated silica inherently contains a coupling agent, use of an additional coupling agent is not believed to be necessary. For example, such coupling agent may be a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of the amorphous silica (e.g. silanol groups) and another moiety interactive with at least one of said diene-based elastomers. Alternatively, said coupling agent may be contained on the silica itself wherein the silica has been pretreated with a coupling agent prior to its addition to the rubber composition.
Representative examples of silica couplers in addition to said organo phosphites are, for example, bis (3-trialkoxysilylalkyl) polysulfides which contain from 2 to 8 carbon atoms with an average of from 2 to 2.6 or from 3.5 to 4 sulfur atoms in its polysulfidic bridge. Representative of such materials are bis (3-triethoxysilylpropyl) polysulfides which contain an average of from 2 to 2.6 or from 3.5 to 4 sulfur atoms in its polysulfidic bridge.
Representative examples of other silica couplers may be organomercaptosilanes such as, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
In another aspect of the invention, said elastomer composition for said non-black colored tread rubber layer(s) and for rubber composition(s) in direct contact with said non-black colored tread rubber layer(s) of is preferably devoid of rubber processing oil other than paraffinic rubber processing oils which contains less than 14 weight percent aromatic compounds and is preferably devoid of antidegradants other than phenolic antidegradants.
In the practice of this invention, said non-black colored rubber composition may be prepared, for example, by mixing in at least one sequential preparatory (non-productive) blending step in at least one internal rubber mixer to a temperature in a range of about 150xc2x0 C. to about 180xc2x0 C. a blend of said diene-based elastomer(s) with said synthetic amorphous silica and/or pre-hydrophobated silica, normally in the absence of sulfur curative, followed by blending the mixture thereof with sulfur curative(s) in a subsequent (productive) blending step in an internal rubber mixer to a temperature in a range of about 110xc2x0 C. to about 120xc2x0 C.
In practice, in the case of using the synthetic amorphous silica, a coupling agent may be added in one or more non-productive (preparatory) mixing steps or divided into an addition in a non-productive (preparatory) mixing step and in a productive mixing step together with the sulfur curative.
The reaction of such agents with the hydroxyl groups on the surface of the silica yields an alcohol such as, for example, ethanol during the manufacture of various silica reinforced rubber products. If such evolution of materials other than alcohol in the manufacture of rubber products would be desired, coupling agents which release water instead of alcohol might be used.